1. Field of the Invention
This invention relates to a pump head for use in connection with pumps for inflating bicycle tires or other inflatable objects, and more particularly to a dual purpose pump head able to be used with both Schraeder and Presta valve stem types.
2. Description of the Prior Art
Virtually every bicycle tube has a valve stem which allows the tube to be inflated and deflated. The two most popular types of valve stems are the Schraeder valve seem and the Presta valve stem, both well known in the art. The Schraeder valve stem generally comprises a hollow cylinder including a depressible valve having an upper or sealed position and a lower or unsealed position. The valve is spring biased into the upper or sealed position to keep air from escaping from the inner tube through the valve. When an inner tube is filled through a Schraeder valve, the pump head is required to have a nipple which depresses the valve against the spring bias to allow air to flow past the valve and into the tube. When the pump head is removed, the spring bias, as well as the internal air pressure, move the valve to the upper or sealed position. The Schraeder valve is very popular on most styles of bicycle inner tubes.
The Presta valve stem is also a very popular valve for use on bicycle inner tubes. The Presta valve stem generally comprises a hollow cylinder (smaller in diameter than the Schraeder valve stem) having a valve at the top end thereof. The valve includes an externally threaded post movably positioned in the hollow cylinder and protruding away from an upper end thereof. An internally threaded nut mates with the external threads on the post, whereby advancement of the nut along the post causes the nut to engage the top of the cylinder, pulling a sealing head on the bottom of the post into a sealing relationship with a seat inside the cylinder. In this position, the post keeps air from leaking out of the inner tube through the valve. When the nut is backed-off or unscrewed along the length of the post, the post is free to slide downwardly into the cylinder until the nut again engages the top of the cylinder, in which position air is free to flow into or out of the inner tube. The post is not spring biased into the sealed position as in the Schraeder valve. When the nut is unscrewed, the air pressure inside the inner tube biases the valve to maintain the sealed position. The nut has notches formed in its sidewalls to allow air to flow through the nut past the post and into the valve, and ultimately into the inner tube.
Application of air pressure to inflate the tube overcomes the tube pressure, and forces the post down into the cylinder until the nut engages the top of the cylinder, allowing, air to flow into the tube through the Presta valve stem.
Currently available pump heads for use in inflating inner tubes having either the Schraeder, Presta, or Italian style valve stems have required either an adapter, or the manipulation of the pump head mechanism to convert it to a suitable configuration for use with the different style valve stems. The prior art pump head version requiring an adapter utilizes the adapter to increase the smaller diameter Presta valve stem to a larger diameter to replicate the size of a Schraeder valve stem. The adapter is a separate piece that is releasably attachable to the upper end of the Presta valve and can be easily lost or damaged, thus affecting, the ability of the user to inflate an inner tube having a Presta valve stem.
Pump heads having convertible mechanisms generally have an inner mechanism which must be removed and reinserted in a different orientation to allow the conversion of the pump head for use with both Schraeder and Presta valve stems. During conversion, the mechanism can be lost or damaged, causing the pump head to be useless in inflating inner tubes having, either the Schraeder or Presta valve stems. Such convertible pump heads are manufactured by A-PLUS Manufacturing of Taiwan, and are available under the brand names TREK or Blackburn, among others.
It is to overcome the shortcomings in the prior art that the present invention was developed.